Generally, thermoplastic resins have lower specific gravity than glasses and metals and can have good physical properties such as moldability and impact resistance. However, many thermoplastic resins can have poor surface scratch resistance.
For example, polycarbonate resins can have excellent mechanical strength, flame retardancy, transparency, and weatherability, in addition to good impact resistance, thermal stability, self-extinguishing property, and dimensional stability. Polycarbonate resins accordingly have been widely used in electrical and electronic products and parts of automobiles. Although polycarbonate resins can be a substitute for products including conventional glasses that require both transparency and impact resistance, polycarbonate resins generally havepoor scratch resistance.
In contrast, polymethylmethacrylate resins can have good transparency, weatherability, mechanical strength, surface gloss, adhesive strength, and excellent scratch resistance. Polymethylmethacrylate resins, however, may not have adequate impact resistance and flame retardancy for various applications.
Conventionally a hard coating method has been used to improve the scratch resistance of plastic products. The hard coating method can include the steps of coating a surface of an injection-molded resin with an organic-inorganic hybrid material and curing the organic-inorganic hybrid material on the surface of the resin using heat or ultra violet light. However, the hard coating method requires an additional coating step, which can increase processing times and manufacturing costs and it may cause environmental problems. With recent increased interest in environmental protection and reduction of manufacturing costs, there is a need for a non-coated resin which has scratch resistance without using the hard coating method. Also, it is important to develop a resin with good scratch resistance for the housing manufacturing industry.
One attempt to improve scratch resistance of thermoplastic resins alloys acrylic resin such as polymethylmethacrylate with good scratch resistance with polycarbonate resin. However, it can be difficult to obtain high transparency and colorability using this method due to the difference between the refractive indices of the polycarbonate resin and the acrylic resin.
Korean Patent Publication Laid-open No. 2004-0079118 discloses a method of lowering the molecular weight of polycarbonate during a kneading process using metal stearic acid ester in order to improve the compatibility between a polycarbonate resin and a methacrylate resin. However, the blend of the polycarbonate and the methacrylate resin can have significantly reduced mechanical properties.
U.S. Pat. No. 4,287,315 discloses a methacrylate resin with good impact strength using an ethylene-vinyl acetate rubber. A blend of polycarbonate and the methacrylate resin, however, can have low transparency.